The present invention relates to a musical-tone signal generating apparatus having a general purpose processor and a processing circuit externally connected therewith, both of which cooperate with each other to perform a process for generating a musical-tone signal and a process for controlling the generated musical-tone signal.
Further, the present invention relates to a musical-tone controlling apparatus which performs on a generated musical-tone signal a musical-tone controlling process including a delay process such as a noise shaping process.
In a conventionally proposed technique, a general purpose processor is employed for generating a musical-tone signal through a software process. A musical-tone signal generating apparatus using the general purpose processor is capable of performing a wider variety of sound-source processes than that employing LSI designed for a special purpose of generating musical-tone signals, and further a reduction in manufacturing costs of the former apparatus can be expected.
The musical-tone signal generating apparatus employing the general purpose processor processes operations of various function keys as keyboard keys and tone-color keys through a general program routine, and generates musical-tone sample data at respective sampling timings through interrupt processes based on timer interrupts caused at predetermined intervals.
The musical-tone signal generating apparatus employing the general purpose processor, however, needs a longer time for executing an arithmetic operation compared with the apparatus employing a special LSI. Accordingly, the musical-tone signal generating apparatus employing only the general purpose processor is not suitable for executing musical-tone control processes which include a rapid arithmetic operation such as an over sampling process, a noise shaping process and dither process.
To overcome the above drawbacks, the general purpose processor is provided with an independent processing circuit externally connected therewith for executing the above musical-tone control processes.
In the apparatus including the externally connected processing circuit in addition to the general purpose processor, when the general purpose processor generates musical-tone sample data through an interrupt service executed at predetermined intervals, a time required for performing a sound-source process to generate the musical-tone sample data at respective timings varies depending on how a program is executed. As a result, the musical-tone sample data are not precisely generated at even intervals. Therefore, timings at which respective musical-tone sample data are generated from the general purpose processor are shifted from timings at which the processing circuit executes the musicaltone controlling process on the respective musical-tone sample data. As described above, the apparatus including the externally connected processing circuit in addition to the general purpose processor has a drawback that allows the musical-tone controlling process to be executed out of synchronism with generation of the musical-tone sample data.
Further, the musical-tone sample data generated by the general purpose processor are temporarily held, for example, in a buffer circuit such as a latch provided in an input portion of a processing circuit, and then are processed by hardware provided in the processing circuit.
Now, consider operation of the conventional musical-tone signal generating apparatus having the above mentioned processor and processing circuit, the operation which is executed when the power is applied.
The processor starts running a predetermined program when the power is turned on, and usually initializes, at the beginning of the program, memories, registers and output latches for outputting the generated musical-tone sample data within the processor, whereby the processor is controlled not to output undesired musical-tone sample data when the power is turned on.
A certain time is needed before the program starts running after the power is applied to the apparatus. Some time (a little time) therefore is required before the above initializing process is executed by means of software.
Meanwhile, since the hardware processing circuit externally connected to the processor starts operation independently of operation of the processor at the time when the power is turned on, contents of the musicaltone sample data held in the input latch provided in the input portion is not kept unchanged for a little time before the above output latch within the processor is reset by means of software.
As described above, the conventional musical-tone signal generating apparatus has drawbacks that the contents of the input latch is processed in the processing circuit, and has the possibility of outputting the resultants through D/A convertor as noise.
Further, when musical-tone controlling processes including a delay process such as the noise shaping process are executed on the generated musical-tone signal, an effect of delay process on the musical-tone signal will be realized as follows: that is, the musical-tone signal at the present sample timing is held in the buffer circuit such as the latch, and is read out at a later sample timing.
In the musical-tone controlling process including the above delay process, a musical-tone signal at the previous sampling timing is delayed by the buffer circuit and is used at the current sampling timing.
It is preferable for the above musical-tone controlling process that when an amplitude of an input musical-tone signal becomes null, the resultant or output signal of the control process becomes null accordingly, but the conventional musical-tone signal generating apparatus has a drawback that even if the amplitude of the input musical-tone signal becomes zero, undesired noise might be output due to signal components previously remaining in the buffer circuit.